Seafarer's Earning Deduction and Higher Rate pension contribution relief

Currently I get basic tax relief on pension contributions through my SIPP provider. I am technically a higher rate tax (40%) payer. Can I retroactively claim the additional 20% pension contribution relief for years when I claimed SED? If so, where do I claim this in SA100?

Hi,
You would have to amend each tax return for 22/23 and 23/24 to declare the gross pension payment in box 1 of page TR4 on SA100.  
For 20/21 and 2022 you would have to submit an overpayment relief claim, following the guidance at SAC12150 (SACM12150 - Overpayment relief: Form of claims).  
It is too late for tax years 19/20 and earlier.
Thank you.